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只是用这两个插件：

apply plugin: 'org.springframework.boot'
apply plugin: 'kotlin'

完整配置：

buildscript {
    ext.kotlin_version = '1.1.2' // Required for Kotlin integration
    ext.spring_boot_version = '1.5.3.RELEASE'
    repositories {
        jcenter()
    }
    dependencies {
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version" // Required for Kotlin integration
        classpath "org.springframework.boot:spring-boot-gradle-plugin:$spring_boot_version"
    }
}

apply plugin: 'eclipse'
apply plugin: 'idea'
apply plugin: 'kotlin' // Required for Kotlin integration
apply plugin: 'org.springframework.boot'
apply plugin: 'application'

写出来的Kotlin调用Java的SpringBoot代码会比较丑：

package org.jetbrains.kotlin.demo

import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication

@SpringBootApplication
open class Application {
    companion object {
        @JvmStatic fun main(args: Array<String>) {
            SpringApplication.run(Application::class.java, *args)
        }
    }
}

每个类，函数上都得标个open。如果要使用Java默认无参构造函数的功能，就要加上

"org.jetbrains.kotlin:kotlin-noarg:$kotlin_version"

我们要写兼容Java的Kotlin代码，当然不会每个类都再手动写个无参构造函数。Kotlin的构造函数跟Java的语法上以及使用方式还是有些不同的。

使用下面的这个配置，代码写起来就自然许多了：

group 'com.easy.kotlin'
version '1.0-SNAPSHOT'

buildscript {
    ext.kotlin_version = '1.1.2-2'
    ext.springboot_version = '1.5.2.RELEASE'

    repositories {
        mavenCentral()
    }
    dependencies {
//        Kotlin Gradle插件
        classpath "org.jetbrains.kotlin:kotlin-gradle-plugin:$kotlin_version"
//        SpringBoot Gradle插件
        classpath("org.springframework.boot:spring-boot-gradle-plugin:$springboot_version")

//        Kotlin整合SpringBoot的默认无参构造函数，默认把所有的类设置open类插件
        classpath("org.jetbrains.kotlin:kotlin-noarg:$kotlin_version")
        classpath("org.jetbrains.kotlin:kotlin-allopen:$kotlin_version")
    }
}

apply plugin: 'java'
apply plugin: 'kotlin'

//Kotlin整合SpringBoot需要的spring，jpa，org.springframework.boot插件
apply plugin: 'kotlin-spring'
apply plugin: 'kotlin-jpa'
apply plugin: 'org.springframework.boot'

sourceCompatibility = 1.8
targetCompatibility = 1.8

repositories {
    mavenCentral()
}

dependencies {
    compile "org.jetbrains.kotlin:kotlin-stdlib-jre8:$kotlin_version"
    testCompile group: 'junit', name: 'junit', version: '4.12'

    compile("org.springframework.boot:spring-boot-starter-web")
    testCompile("org.springframework.boot:spring-boot-starter-test")
    compile("org.springframework.boot:spring-boot-starter-data-jpa")
    compile('mysql:mysql-connector-java:5.1.13')

}

代码就可以这样写了：

package com.easy.kotlin

import com.easy.kotlin.entity.People
import com.easy.kotlin.service.PeopleService
import org.slf4j.LoggerFactory
import org.springframework.boot.CommandLineRunner
import org.springframework.boot.SpringApplication
import org.springframework.boot.autoconfigure.SpringBootApplication
import org.springframework.context.annotation.Bean
import java.util.*

/**
 * Created by jack on 2017/6/7.
 */


@SpringBootApplication
class Application {

    private val log = LoggerFactory.getLogger(Application::class.java)

    @Bean
    fun init(repository: PeopleService) = CommandLineRunner {
        val now = Date();
        repository.save(People(null, "Jason", "Chen", "Male", 28, now, now))
        repository.save(People(null, "Bluce", "Li", "Male", 32, now, now))
        repository.save(People(null, "Corey", "Chen", "Female", 20, now, now))

        for (people in repository.findAll()!!) {
            log.info(people.toString())
        }

        val customer = repository.findOne(1L)
        log.info(customer.toString())
        for (chen in repository.findByLastName("Chen")!!) {
            log.info(chen.toString())
        }
    }

}

fun main(args: Array<String>) {
    SpringApplication.run(Application::class.java, *args)
}

示例工程源码：

https://github.com/EasyKotlin/easy_kotlin_chapter2_hello_world_springboot_restful